1. Field of the Invention
This invention relates to light emitting devices including a radiation source, and an excitable phosphor. It more specifically relates to the application of a class of chemical compounds for use as phosphors for the conversion of radiation into visible light in light emitting devices.
2. Discussion of the Art
Lanthanide-based phosphors have applications in multi-component phosphor lighting applications. Current lanthanide-based inorganic phosphors such as Y2O3:Eu and LaPO4:Ce, Tb, typically absorb 254 nm radiation effectively. For this reason, the lanthanide-based inorganic phosphors are useful in mercury discharge applications, such as fluorescent lighting. However, new high-efficiency light sources, such as light emitting diodes (LEDs), require phosphors that readily absorb near ultraviolet radiation in the 300-460 nm range where conventional lanthanide-based inorganic phosphors typically do not strongly absorb.
LEDs and laser diodes (LD) have been produced from Group III-V alloys such as gallium nitride (GaN). To form the LEDs, for example, layers of the alloys are typically deposited epitaxially on a substrate, such as silicon carbide or sapphire, and may be doped with a variety of n and p-type dopants to improve properties such as light efficacy. With reference to the GaN-based LEDs, light is generally emitted in the UV and/or blue range of the electromagnetic spectrum.
Recently, techniques have been developed for converting radiation emitted from LEDs to useful light for illumination purposes. By using a phosphor excited by the radiation generated by the LED, light of different wavelengths may be generated to produce desired color points. For example, a combination of LED generated radiation and phosphor converted light may produce visible light (e.g. white). There are few known lanthanide-based phosphors which readily absorb in the UV wavelength region and have efficient luminescence in the visible spectral region. This is especially true for narrow-band red phosphors.
The known lanthanide phosphors which are applicable for lighting applications are solid state compounds, such as Y2O3:Eu, which readily absorb radiation below 300 nm, in the far UV range. Solid state compounds have specific ligands which can not be easily varied on the molecular level. In contrast, the use of a molecular compound permits the facile manipulation of the ligands on the molecular level, which allows the compound to fulfill the design criteria for a given application.
A class of lanthanide-based molecular compounds which will act as phosphors capable of readily absorbing electromagnetic radiation and converting that radiation to visible light is therefore desirable.
In an exemplary embodiment of the present invention, a light emitting device is provided. The light emitting device includes a light emitting component and at least one phosphor material. The phosphor material absorbs electromagnetic radiation emitted by the light emitting component and converts that radiation to visible light of the desired color.
The use of a lanthanide based molecular compound as a phosphor composition in lighting applications is described. The phosphor composition contains a lanthanide, Ln; xcex2-diketonate ligands, A; and at least one additional ligand, B. The components of the phosphor composition are combined in accordance with the formula LnAXBY, where X and Y are integers ranging from about 1 to about 10.
A light emitting device containing a light source and a phosphor is provided. The phosphor is a molecular compound of the formula LnAXBY, where Ln is a lanthanide, A is xcex2-diketonate ligands, B is an additional ligand, and X and Y are integers ranging from about 1 to about 10.
A primary benefit of the invention resides in the ability to vary the components of the phosphor composition on the molecular level to fulfill the design criteria for a given application.
Another primary benefit of the invention resides in the efficient luminescence in the visible spectral region.
Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the various embodiments.